Field of the Invention
This technology relates to a page buffer of a memory array.
Description of Related Art
Programming a memory cell relies on multiple programming pulses, such as via ISPP (incremental step pulse programming). Different memory cells across an array may behave non-uniformly during programming for various reasons such as variations in manufacturing, temperature, voltage, and disturb effects. Because of such lack of uniformity, different memory cells require a different number of programming pulses, despite nominally starting the program operation from the same beginning logical level and nominally ending the program operation at the same finishing logical level. This can be displayed by a threshold voltage distribution graph of number of memory cells versus threshold voltage, which shows that a relatively non-uniform group of memory cells has a wide, short distribution, and that a relatively uniform group of memory cells has a narrow, tall distribution.
The relatively non-uniform group of memory cells requires more program and verify cycles than the relatively uniform group of memory cells. Accordingly, there is a wide variation in the duration of programming any individual memory cell or group of memory cells, even for memory cells that share the same nominal beginning logical level and the same nominal finishing logical level.
It would be desirable to adjust how memory cells are programmed, to reduce the variation in the duration of programming. It would also be desirable to reduce the duration of programming, even for a relatively non-uniform group of memory cells.